A friend bought an f2.0 Summicron-M Aspheric for his M7 last year for $1,650.00 AUD last year.
I don't know where he bought it from, but I know that's what he paid for it.
The reason I know this, is because he sold his old Subaru ute for $1,500 to pay for it and needed a loan of $150.00 which he got from his very understanding girlfriend.
That should give you a ball park figure, but this lens was, I believe, on the cheap side, which is why he sold his ute to a car yard inside ½ an hour of hearing about this lens being for sale, then he rang his girlfriend, who happened to be in my darkroom when she took the call.
I'm basically a Nikon person, that is about the extent of my current Leica knowledge.